Integrated Services Digital Network (ISDN) uses digital telephony services offered by regional telephone carriers to provide a global WAN which can be used to transmit network data. Two types of ISDN services exist, namely ISDN BRI (Basic Rate Interface) and ISDN PRI (Primary Interface). ISDN BRI offers connection speeds up to 128 Kbps while ISDN PRI services offer connections ranging up to 2.048 Mbps (or 1.554 Mbps)
ISDN BRI network includes two 64 Kbps channels (called B channel), and one 16 Kbps channel (called D channel). B channel carry data, digitalized voice, or digitalized video signals. The D channel is service channel used for both data and control information. ISDN BRI is ideal for home and small businesses that need data transfer rates higher than traditional modems. See also Diva ISDN USB Terminal adapter for BRI.
There are two scenarios you can use with this ISDN BRI network:
- One B channel is dedicated to voice, and the other B channel is dedicated to data
- Both B channels are dedicated to data for a total transfer rate of 128 Kbps
The total bandwidth of an ISDN BRI line is 144 Kbps (two B channels and one D channel) with total data transfer rate is 128 Kbps.
ISDN BRI Practical Applications
ISDN BRI is a relatively low-cost WAN service that is ideal for the following situations:
- Home office or telecommuters who need a relatively fast connection
- Businesses that need to periodically send data between sites (burst traffic pattern)
ISDN BRI offers the following benefits over dial-up modems and other WAN connection options.
- Faster data transfer rates (128Kbps) compared to dial-up modems (56Kbps maximum)
- Faster call establishment (dial-up) than modems
- Lower cost than other WAN solutions (users pay a monthly fee plus connection charges)
However, although gaining in popularity, ISDN is not available in every market.
Because ISDN BRI must establish a connection to transfer data, it is not a good solution where fast, constant connections are required. In addition, as the use of the ISDN BRI line increases, connection charges will also increase. At some point, it will be more economical to pay the higher monthly fees for another WAN service.
ISDN BRI Function groups and reference points
ISDN BRI Connection
Routers A and B represent typical cabling with a Cisco router, using ISDN, in North America. Router A is ordered with an ISDN BRI U interface; the U implies that it uses the U reference point, referring to the I.430 reference point for the interface between the customer premises and the telco in North America. No other device needs to be installed; the line supplied by the telco is simply plugged into the router’s BRI interface.
Router B uses a BRI card with an S/T interface, implying that it must be cabled to a function
group NT1 device in North America. An NT1 function group device must be connected to the telco line through a U reference point in North America. When using a router BRI card with an S/T reference point, the router must be cabled to an external NT1, which in turn is plugged into the line from the telco (the U interface).
Both Router A and Router B use an ISDN BRI card, but they have different reference points. A router can connect to an ISDN service with a simple serial interface, as shown with Router C in the above diagram. Router C must implement an ISDN function group called TE2 (Terminal Equipment 2) and connect directly to a device called a terminal adapter using the R reference point.
Configuring ISDN BRI
Configuring ISDN BRI is a relatively easy task to do, you just need to complete the following task:
1. Set the ISDN switch type in global configuration mode on in the interface mode, it can be one of this list below:
a. basic-1tr6 – 1TR6 switch type for Germany
b. Basic-5ess – AT&T 5ESS switch type for USA
c. Basic-dms100 – northern DMS-100 switch type
d. Basic-net3 – NET3 switch type for UK and Europe
e. Basic-ni – National ISN switch type
f. Basic-ts013 – TS013 switch type for Australia
g. Ntt – NTT switch type for Japan
h. Vn3 – VN3 and VN4 switch type for Frances
2. Configure SPIDs (if required), use spid1 and spid2 commands to identify the SPIDs for a specific interface.
In addition to complete ISDN BRI configuration you need to complete the following tasks:
- Assign the IP address to the interface
- Configure PPP encapsulation
- Configure dial-on-demand routing
- Configure static route
The following table summarizes commands for configuring ISDN BRI:
| Identify remote routers and passwords for PAP or CHAP: | Router(config)# username <hostname> password <password> |
| Enter ISDN BRI interface configuration mode: | Router(config)#int bri 0 |
| Set PPP encapsulation | Router(config-if)#encap ppp |
| Set the PPP authentication method (PAP or CHAP) | Router(config-if)#ppp authentication <method> |
| Set the ISDN switch type (depends on the switch type used by the service provider). If you use the IOS v. 11.3 and higher – use interface mode; if you use IOS v.11.2 and below – use global config mode. |
Router(config-if)#isdn switch-type <type> (interface mode) or
Router(config)#isdn switch-type <type> (global config mode) |
| Assign SPIDs to the interface (use only if the SPIDs are not dynamically assigned and detected by the system) |
Router(config-if)#isdn spid1 <number> <number>
Router(config-if)#isdn spid2 <number> <number> |
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